Many illnesses or conditions require administration of a constant or sustained level of a medicament or biologically active agent to provide the most effective prophylactic or therapeutic effect. This may be accomplished through a multiple dosing regimen or by employing a system that releases the medicament in a sustained fashion.
Systems for delivering sustained levels of medication have employed biodegradable materials, such as polymers, encapsulating the medicament. The use of biodegradable polymers, for example, in the form of microparticles or microcarriers, provides a sustained release of medicaments, by utilizing the inherent biodegradability of the polymer to sustain the release of the medicament. The ability to provide a sustained level of medication can result in improved patient compliance.
Certain methods of fabricating polymer-based sustained release devices comprise the steps of dissolving a polymer in a solvent, adding to the polymer solution the active agent to be incorporated and removing the solvent from the mixture thereby forming a matrix of the polymer with the active agent distributed throughout the matrix.
However, many of these sustained release compositions can exhibit an increased release of biologically active agent over the first twenty-four hours after administration, commonly referred to as a burst. In some instances, this burst can result in an undesirable increase in the levels of biologically active agent and/or minimal release of agent thereafter. Therefore a need exists to exert additional control over release kinetics by, for example, reducing the burst of agent and/or providing an improved release profile.